1. Field of the Invention
This invention relates generally to heat recovery systems and particularly to such systems which recapture and reburn the wood gases from a wood carbonizing facility for direct application to an end use facility such as wood drying kilns.
2. Discussion of Related Art
Historically, conversion of low-grade hardwood and saw mill scrap to charcoal and/or heat energy has been carried out through processes that were primarily suited to produce either charcoal or heat energy with little effort to salvage or market the other. Also, these processes usually require large investments in machinery and are not economically feasible for small to medium sized saw mills. These mills normally cannot justify the investment and/or operating costs necessary to dry lumber and are therefore limited by weather conditions, financial resources or market conditions, including market size and production volume available. Accordingly, a need has arisen for disposing of waste wood products in an economical, practical and environmentally safe manner.
U.S. Pat. No. 649,757, issued May 15, 1900, to Robertson, shows a lumber drying facility wherein the exhaust steam of the engine of a lumber mill is utilized to afford heat in the drying kiln. U.S. Pat. No. 1,083,813, issued Jan. 6, 1914, to Farrell, also shows the concept of utilizing waste heat produced in a production facility for subsequent product drying. U.S. Pat. No. 1,423,136, issued July 18, 1922, to Mueller, shows yet another system wherein waste heat is recirculated to provide a drying medium for use in a kiln. Mueller's waste heat is derived from the exhaust steam from a steam driven motor used for producing a positive circulation of the drying air. U.S. Pat. No. 1,499,976, issued July 1, 1924, to Friderichsen, shows a heating system which utilizes the waste heat generated in drying kilns for the heating of buildings, drawing rooms, and the like. However, none of these patents shows a system whereby scrap wood from lumber mills is used to produce both saleable charcoal products and products of combustion which are used in drying kilns.
There also exist many suggested types of combustion chambers for use as afterburners. For instance, U.S. Pat. No. 3,192,905, issued July 6, 1965, to Barnes, shows a carbon monoxide oxidizer and fluid heater which makes use of a cylindrically shaped combustion chamber having a circular lower section with tangentially connected gas inlet ports and an intermediate venturi like restricted diameter mixing section with a circular upper combustion section. U.S. Pat. No. 3,194,215, issued July 13, 1965, to Barnes, shows a similar carbon monoxide burner apparatus having a cylindrical combustion chamber with internal refractory lined walled portions, a lower flue gas inlet section, and an upper gas combustion section having a hot gas outlet passageway in a restricted diameter gas mixing zone positioned between the inlet gas section and the upper combustion section. U.S. Pat. No. 3,423,928, issued Jan. 28, 1969, to Walsh, discloses an afterburner comprising a perforated venturi throat to draw air into the stream of exhaust in a fuel nozzle positioned downstream from the venturi throat. The nozzle is of the fuel aspirating type wherein the passage of gases therethrough draws fuel into the nozzle. Other suggested afterburners include those shown in U.S. Pat. No. 3,754,869, issued Aug. 28, 1973, to Van Raden, and U.S. Pat. No. 3,930,802, issued Jan. 6, 1976, to Beasley et al.